To detect the current magnitude of a current flowing through a conductor, in addition to shunt resistors that are subject to the disadvantages of energy losses and the lack of potential separation, current sensors are also known that detect the magnetic field generated by the current flowing in the conductor. For this purpose, in particular, Hall sensors and induction coils are used in the prior art.
Hall sensors are based on the Hall effect, wherein a current flowing in a solid body (usually a semiconductor crystal) is deflected by the Lorentz force perpendicular to the current and magnetic field direction. They can also detect direct currents. One weakness of Hall sensors, however, is a relatively high noise component in the signal, especially at higher frequencies. In addition, Hall voltages are dependent on temperature, because the offset (output voltage when there is no magnetic field) and the sensitivity or amplification (output voltage per magnetic flux) change as a function of the respective temperature of the Hall sensor.
In contrast, induction coils detect the change in the magnetic field over time. By nature they are not suitable for detecting direct currents.
In the prior art, it was proposed to equip current sensors with combinations of Hall sensors and induction coils:
According to SI 98 00 063 A, a Hall sensor and an induction coil are arranged adjacent to a conductor. The signals of the Hall sensor are passed through a low-pass filter, while the signals of the induction coil are integrated in time and passed through a high-pass filter. The time constants of the high-pass and low-pass filters match. The output signals of the low-pass and high-pass signals are summed together. The low-frequency components of the current through the conductor are thus detected by the Hall sensor and the high-frequency components are detected by the induction coil. Here, there is nevertheless the problem of the temperature dependency of the sensitivity and the offset of the Hall sensor.
DE 10 2008 030 411 A1 likewise uses a Hall sensor and an induction coil, in order to detect the magnetic field of a conductor constructed as a coil. The signals of the Hall sensor are fed to a low-pass filter and also the signals of the induction coil are passed through a low-pass filter. The output signals of both low-pass filters are each added together after multiplication with an associated weighting factor. Another coil adjacent to the Hall sensor is connected to a control unit. If there is no measurement current in the conductor, the additional coil (or the induction coil) is loaded with a current, in order to calculate the offset and amplification error using the output voltage of the Hall sensor that is then produced, and these values are then considered in the signal processing. In addition, a temperature sensor can measure a possible change in temperature, in order to compensate for a resulting drift in the offset or the sensitivity of the Hall sensor. The temperature sensor increases the complexity and requires a precise calibration for compensating for the temperature dependency of the signals of the Hall sensor, while loading the Hall sensor with the magnetic field of the additional coil or the induction coil is possible only when there is no measurement current and thus it is not possible continuously.
Thus, it is desired to provide an improved current sensor.